The Influence of Emotionally Linked Odors on Autonomic Nerve Activities

The limbic system, supporting emotions, behavioral motivation, and memory, in the brain receives coming odor before the sensory cortex. Therefore, certain odor can affect autonomic nerve system and physiological parameters due to smell-induced activity in the limbic system. The purpose of this study focused was to investigate the influence of odor, taking the level of arousal and valence into account, on autonomic nerve activities and physiological parameters. Eight healthy young males (20.6 ± 0.5 yr), who gave a response of high arousal (6.8 ± 0.5) and negative valence (1.5 ± 0.8) to the odor of vinegar (VNG), and an opposite response (arousal 2.3 ± 0.8, valence 6.6 ± 0.4) to the odor of orange (ORG), were selected as subjects. Heart rate and its variability (HRV), and blood pressure (BP) were evaluated for the subjects who were quietly seated, wore a plastic mask with a vapored odor-injection pipe, and breathed naturally the two aromas (VNG, and ORG). A no aroma condition was also included in the test as a control. Repeated measures ANOVA with a Turkey post-hoc test revealed a significant odor effect in the variables of HRV, and BP. VNG led to a higher ratio of low frequency /high frequency (LF/HF), and lower HF compared to the control (p < 0.05, p < 0.05, respectively). VNG also had significantly higher diastolic and mean BP than ORG (p < 0.05, p < 0.05, respectively). ORG, on the other hand, failed to show any significant odor effect on HRV and BP variables. LF/HF can be a sympathetic nerve activity indicator while HF is known as a para-sympathetic nerve activity indicator. Our results of breathing VNG thus suggests that odors causing negative valence and high arousal can facilitate sympathetic nerve activity, and/or withdraw para-sympathetic nerve activity. A higher BP with VNG compared to ORG can also be attributed to the effect of these autonomic nerve activities. Consider all the various factors together, it can be concluded that some emotionally linked odors were strong enough to modulate autonomic nerve activities as well as the level of BP in resting individuals.